1. Unilateral recurrent laryngeal nerve paralysis
Unilateral vocal fold paralysis leads to insufficient glottis closure with air loss
in the context of speaking, reduction of the voice range, pitch and volume,
reduction of the maximum phonation time and audible breathiness of the voice. The
result is a weak voice that tires quickly and the risk of pathological compensation
of the insufficient glottis closure by using the false vocal folds. The severity of
the complaints mainly depends on the position and tension of the vocal folds.
Initially, the voice may be aphonic and proneness to aspiration may be observed.
In daily routine, less attention is paid to the fact that at the same time a
unilateral abduction inhibition exists that limits the max. diameter of the glottic
opening. In cases of unfavorable, widely median position and high tension, some
patients complain about breathing difficulties in the context of high physical
exercise.
In most cases, compensation or ideally even complete restoration of the motility may
be achieved. The focus of this article is placed on those cases where conservative
speech therapy does not lead to sufficient improvement and bioimplants are applied
for vocal fold medialization.
1.1 Injection laryngoplasty
The term of injection laryngoplasty defines the injection of biomaterials or
autologous tissue transfer into paralyzed vocal folds for augmentation of the
vocal fold volume with the objective to restore a complete glottis closure for
phonation. According to Choi et al. [1],
the benefit from augmentation is significantly increased in younger patients
(<65 years) and those with mild glottis gap. This authors defined the
glottis gap as mild when the distance between the vocal processes was smaller
than half of the width of the healthy vocal fold.
The German ENT surgeon Brünings is considered as the founder of injection
laryngoplasty. Already in 1911, he described the augmentation of the vocal fold
with paraffin oil [2]. In 1985 for the
first time, Teflon injection into the vocal folds was performed in awake
patients under local anesthesia in the USA [3]. The technique of Teflon injection was applied very frequently in
the 20ies century because it was technically well applicable and had a lasting
augmentation effect, however, due to the relevant number of giant cell
granulomas, this approach was abandoned [4]. Teflon granulomas as foreign body reaction may develop even decades
after injection. The inflammation only stops when the Teflon and the surrounding
granulation tissue are completely removed. The long-term sequelae for the voice
seem to be obvious.
The ideal substance for vocal fold augmentation has not yet been found. Not all
routinely applied substances for vocal fold augmentation have been developed for
application in the larynx. Due to the missing conformity confirmation of the
European Community (CE, Communauté Européenne), their usage is
considered as therapeutic application of biomaterials outside the indication
spectrum (off-label use), even in cases of existing FDA approval (Food and Drug
Administration). According to the author’s experience, the frequently
used classification into temporary and permanent injection materials is not
finally clarified. The data situation in the literature regarding resorption
rate, effect duration, and biological interaction of the autologous, xenogenic,
and alloplastic substances that are currently applied for injection
laryngoplasty are still insufficient. In a meta-analysis published by Wan-Chiew
et al. in 2021 [5], the authors assessed
6,240 publications on biomaterials that have been developed for vocal fold
augmentation since 2010. The authors concluded that statements on the
viscoelasticity are made without referencing them to the clinical effect.
Studies about the biological absorption (effect duration), cell interaction, and
inflammatory reactions (side effects), however, are insufficient and should be
initiated in time when future augmentation materials are developed.
1.1.1 Temporary vocal fold augmentation
Within 4–6 months, up to 75% of the patients with unilateral
paralysis regain phonation that is sufficient for their vocal needs although
the percentage of the vocal fold motility restoration is significantly lower
(33–40%). However, in clinical routine there are a number of
patients who do not achieve a satisfactory glottal closure with speech
therapy allone but develop a compensatory hyperfunction with excess use of
supraglottic sphincters. Besides, there is a growing number of patients who
professionally use their voice and who have high demands to the restoration
of the voice function. In these cases, the option of temporary vocal fold
augmentation should be discussed early. In accordance to Hess et al. [6], we started to offer this therapy
option already at the time of diagnosis. In this way, the subsequent speech
therapy is facilitated, the patients can work earlier in their
voice-depending job and perceive the improvement of their voice quality
directly after the diagnosis of a paralysis.
During the last century, numerous materials have been tested and applied for
temporary vocal fold augmentation. Materials with short-term effect are
fibrin glue that is nowadays used rather for vocal fold scars and
phonosurgery and bovine gelatin that is preferred in the USA (Gelfoam,
Surgifoam) and that has mostly been replaced by carboxymethyl cellulose
(Radiesse Voice Gel) [7]. None of these
materials is CE approved.
Collagen and hyaluronic acid materials are considered as having an
intermediate effect (see [Fig. 1]).
Their effect duration is often given with 3–4 months. Even longer
augmentation effects have been observed in clinical practice.
Fig. 1 Temporary augmentation of the vocal fold with
hyaluronic acid or similar temporary fillers.
The application of bovine collagens (Zyplast, Cymetra and others) requires
compatibility testing three weeks before use. The reason for this previous
skin test is the risk of type IV allergic reactions because about 3%
of the population are already sensitized against bovine collagen before
collagen treatment. The augmentation with this biomaterial should not be
performed by injection into the muscles but into the lamina propria because
resorption occurs more quickly in the muscles. In cases of superficial
injection into the vocal fold, inflammation in Reinke’s space may
develop with restriction of the mucosal wave and subsequent organic
dysphonia [8]. In medicine, porcine
collagens are applied rather as matrix materials for example for camouflage
of the nasal dorsum in rhinoplasty (Permacol). However, they cannot be used
in all patients, also due to religious reasons. Alternative options are
human recombinant collagens that are gained transgenically via plants or
bacteria (CosmoPlast/CosmoDerm) [9]. Due to their instability, they are mostly combined with
hyaluronic acid in plastic surgery [10].
Due to the disadvantages of collagens, predominantly hyaluronic acid
preparations are currently used (Restylance, Hyalaform, Juvederm, and
others) for temporary vocal fold augmentation [11]
[12]
[13]
[14]
[15]. Depending on the chosen brand, hyaluronic acid is mostly
well tolerated, has a suitable viscosity, and allergy tests prior to
application are not necessary. Preparations from this substance group are
frequently used in esthetic surgery as fillers for wrinkle treatment.
Therefore, a lot of experience regarding tissue tolerance is available.
According to the author’s knowledge, these preparations are CE
certified but none of them has been approved for the indication spectrum of
vocal fold augmentation. This means that the application of this important
group of substances is currently also off-label. Patients must be informed
comprehensively about this circumstance. If augmentation of the vocal folds
with these off-label substances is the only reason for treatment, there
might be problems with reimbursement by the health insurances.
Calcium hydroxyl apatite microspheres (Renu Voice) is another substance
coming from the field of esthetic wrinkle treatment. It was specifically
approved for vocal fold augmentation based on CE criteria and may thus be
applied in-label. In a recent article by Miaskiewicz et al. [16], the authors compare the long-term
effect of hyaluronic acid (HA) with calcium hydroxyl apatite (CaHA). They
found a surprisingly long-lasting effect of both substances over the
follow-up period of 24 months. Only in 12.5% of the CaHA and in
9.3% of the HA augmentations, re-augmentations were necessary. These
results may be interpreted in two different ways. On one hand, the
resorption time of HA and CaHA might have been estimated wrongly in the
vocal fold tissue. The present studies on the resorption of HA refer to
esthetic application in the face and of CaHA to animal experiments [17]
[18]. On the other hand, re-innervation starting in parallel to
the partial or complete resorption of the augmentation materials may
contribute to better toning and volume increase of the vocal fold, even if
it does not lead to restoration of the motility, and thus mimic a residual
augmentation effect. Histological examinations in this field are not
available.
An intermediate position between temporary and permanent augmentation may be
assumed by substances that may cause volume preservation or increase of the
vocal fold by interaction with the tissue. This group of substances includes
growth factors like the basic fibroblast growth factor (bFGF) that,
according to animal experiments, increases the number of end plates in the
re-innervation phase of recurrent laryngeal nerve paralyses and is said to
have a regenerative effect on nerve and muscle fibers. In the
placebo-controlled trial performed by Hirano et al. [19], a significant cross-section
increase of the thyro-arytenoid muscle could be observed within 4 weeks. An
increase of the autogenous hyaluronic acid production in the lamina propria
could be confirmed by Kanazawa [20] for
scars, sulcus, and paralyses. However, the author of this contribution does
not know about any application of xenogeneic or recombinant human fibroblast
growth factors in humans in Europe for this purpose [21]. Growth factor inhibitors are
approved for the field of oncology. Beside the growth factors, pluripotent
stem cells and especially mesenchymal stem cells from fatty tissue (ASC)
might play a role for the regeneration of vocal fold paralyses [22] in the future. In order to avoid
excessive scar formation after phonosurgical interventions for
reconstruction of the vocal folds, such lipid fraction containing stem cells
are already applied [23].
1.1.2 Permanent vocal fold augmentation
Despite the limiting factor that important resorption has to be considered
also for these materials, augmentation of the vocal fold by means of
autologous fat or fascia is classified as permanent procedure. Generally,
permanent augmentation should only be applied when spontaneous recovery of
the recurrent laryngeal nerve paralyses can no longer be expected or
persistent damage of the nerve due to previous diseases or surgeries is
known.
Autologous fat is biocompatible, cheap to gain, and non-toxic [24]. The disadvantage is the initial
resorption rate that cannot be predicted. Therefore, in general
over-correction is planned. For extraction of fat material, there is the
early applied procedure of manual taking of small fat portions by means of
scalpel and washing out of lipid cells. In plastic surgery, the objective
was to separate cellular debris and liquid from intact fat cells that should
be transplanted preferably. Due to the diameter of the injection cannulas
(18–20 G) and the mechanical stress of the transplanted
material in the vibrating vocal fold, this procedure must be considered as
rather hypothetic. In the last years, the manual preparation was abandoned
and replaced by periumibilical liposuction. Hereby, the extracted fat is
centrifuged with 3,000 rpm for 3 minutes [25]. This method is applied in plastic
surgery and is suitable for production of well injectable biomaterial for
application at the vocal fold. By separating the material into three
fractions, the heavy cellular debris remains on the bottom of the syringe,
in the middle the fat and stem cells are found, and on the top the lighter
fat. Only the middle part is used for augmentation. For this method, a
specific set for extraction and injection is provided (VoiceInject) [26]. Compared to all permanent
augmentations, the injections are generally performed in the context of
microlaryngoscopy under general anesthesia (see [Fig. 2]). However, in cases of risks
for general anesthesia it is also possible to perform fat extraction under
tumescence anesthesia and the injection by flexible endoscopy under sedation
[26]. Due to the long way through
the injection catheter needle inserted in the working canal (23 G),
more fat is required, and a high-pressure pistol must be used for insertion
of the material. According to our experience, the effect duration varies
enormously. After 12–24 months, re-augmentation must be
expected.
Fig. 2 Fat augmentation into the thyroarytenoid muscle (TA) in
several deposits (yellow); overcorrection due to fat resorption must
be considered.
A similar approach is pursued with the application of pieces of autologous
temporalis fascia or fascia lata [27].
The manual preparation until injection is more extensive compared to fat but
especially regarding long-term stability the results are better. Gneid et
al. [28] describe an effect duration of
3–10 years in more than 500 interventions which is significantly
longer than with fat and has the same tolerance. Nonetheless, this method
could not prevail, probably because of the extensive preparation and the
risk of blocked cannulas. Currently, the application of fascia, fat,
perichondrium, cartilage in combination or together with growth factors is
further investigated in animal experiments or clinically in cases of scars
or wounds of the vocal folds. It remains to be seen which autologous
material will have the most important clinical significance in the
future.
Regarding alloplastic biomaterials for permanent vocal fold augmentation, the
use of polymethyl dioxane (silicone) micro particles in suspension (Vox
Implants) must be mentioned [29]
[30]
[31]
[32]. The material has
the effect of permanent augmentation but stiffens the area of the vocal fold
around the injection site. To a certain extent, it may also be applied for
correction of the position of the arytenoid cartilage. The material
originates from the discipline of urology (UroPlast) and was CE certified
for the indication of permanent vocal fold augmentation with the brand name
of Vox Implants. Therefore it may be applied in-label. Generally, the widely
lateral injection between the thyroid cartilage and the muscles is important
in order to avoid stiffening of the vocal fold and to ensure good tissue
compatibility (see [Fig. 3]). To avoid
misplacement and to preserve the option to well distribute the biomaterial,
the application is recommended to be performed under general anesthesia in
the context of microlaryngoscopy.
Fig. 3 Permanent augmentation with silicone microspheres
(VoxImplant – whitish) widely lateral between the thyroid
cartilage, lateral thyroarytenoid muscle (LCA), and thyroarytenoid
muscle (TA).
This alloplastic material is highly biocompatible, non-toxic, and the costs
are acceptable in comparison to thyroplasty. Especially for older patients
with bronchial or esophageal carcinomas with aspiration disorders, injection
laryngoplasty with Vox Implants provides a rapid therapy option. Granulomas
as caused by Teflon or severe foreign body reactions provoked by GoreTex are
not known with a correct lateral injection. However, the silicone particles
induce connective tissue reaction. Smaller quantities may be taken outside
the larynx by macrophages and deposited. The connective tissue in the
neighborhood of polymethyl dioxane particles may mimic a tumor disease in
the FDG-PET examination [33]
[34]. In cases of necessary permanent
augmentation for patients with curative treated malignant diseases of the
larynx, hypopharynx, or thyroid gland, Vox Implants is contraindicated and
autologous fat is preferred which can be well differentiated from tumors in
MRI and PET-CT scan. If paralysis of the opposite focal fold may occur, Vox
Implants should not be applied because the surgical removal of the material
is rather difficult.
An intermediate position between injection laryngoplasty and medialization
thyroplasty is assumed by the insertion of polytetrafluoroethylene (GoreTex)
straps between the thyroid cartilage and the paraglottic muscles for
permanent medialization of the vocal fold. This procedure is predominantly
applied in the USA. The surgeon individually cuts the straps from a patch
manufactured for pericardial reconstruction or vascular surgery and insert
it through a small anterior thyroid window [35]. Even an approach from the inferior edge of the thyroid
without window has been described [36].
So, it is neither an injection technique in the proper sense of the word,
nor a typical thyroplasty. The advantage of this method is the
individualized medialization adapted to the patient’s needs.
Especially the anterior third of the vocal fold can be better augmented.
Applications after substance defects of the vocal folds have also been
described. These favorable properties, however, are overshadowed by numerous
reports about inflammation and rejection reactions requiring the removal of
the material in revision surgeries [37]
[38]. These experiences
have previously also been made at the occasion of the use for camouflage for
rhinoplasties [39]. In any case, the
material is not CE approved for extracardiovascular applications and the
biomaterial that is offered only in large dimensions is very expensive.
1.2 Medialization laryngoplasty (ML)
The objective of the procedures described here is the permanent medialization of
irreversibly paralyzed vocal folds in order to restore the complete glottis
closure during phonation. The first description of the term of thyroplasty dates
back to 1974 and the classification of phonosurgical interventions at the
thyroid cartilage was introduced by Isshiki [40]. He was the first to describe in a dog model the lateral
compression of the endolarynx in cases of paralysis by vertical incision of the
thyroid cartilage and stepwise inward placement of the posterior two thirds as
thyroplasty type I. One year later, he published the creation of a
thyroid cartilage window in humans on the level of the vocal fold with an
autologous thyroid graft [41]. A proposal
of a classification made by the European Laryngological Society (ELS) in 2001
summarized the procedures of thyroplasty type I and arytenoid adduction as
approximation laryngoplasty [42]. However,
this classification could not prevail up to now.
1.2.1 Autologous implants
Already in 1915, Payr described vocal fold medialization with autologous
thyroid cartilage [43]. This principle
was taken up again and again, in the 1950s by Opheim [44], in the 1970s by Isshiki [41], in the 1980s by Kleinsasser [45], and even currently [46]
[47] with several modifications. Beside thyroid cartilage, also
the use of rib cartilage [48], nasal
septum and ear cartilage [49]
[50] have been mentioned while no
advantage could be shown in comparison to thyroid cartilage that is
available at the surgery site.
The advantages involve the high biocompatibility even in children, the simple
resection at the surgery site without additional costs and the certainty
that foreign body reactions in subsequent imaging do not cause artifacts. In
general, the disadvantages include a limited adjustability due to the given
thickness of the cartilage, and risks of dislocation and cartilage
resorption decreasing the effect of the thyroplasty. Also, the effect on a
posterior gap is limited. The cartilage removal at the upper edge of the
thyroid may lead to postoperative hematoma, airway swelling, and swallowing
problems. The significant issue of resorption could not yet be clarified
satisfactorily. In 1995, Tucker conducted a thyroplasty trial with dogs
using autologous thyroid cartilage. Histology after 6 months revealed an
acceptable volume loss of 13%. Other authors report about clinical
experience with higher rates. Already Isshiki emphasized the careful use of
the tissue and the importance of preserving the perichondrium at the
cartilage in order to secure nutrition of the cartilage [51]. Experienced surgeons may still
apply this method, especially when patients are reluctant with regard to
foreign material for thyroplasty.
1.2.2 Silicone implants
Already very early, alternatives for autologous cartilage have been
investigated for thyroplasty type I. Initially, the cartilage of the
thyroplasty window was further used with its perichondrium as stamp; and
foreign material was applied for locking and later also for V-shaped
adaptation of the medialization effect under auditive control in surgeries
performed in local anesthesia [52]
[53]. Most widely used are medical
silicone blocks that are individually cut during surgery [54]. The advantage consists of the
individual shaping with consideration of the sex-specific thyroid angle
[55], the length of the thyroid
ala, and the malposition of the paralyzed vocal fold that shall be corrected
(see [Fig. 4]). As in all
below-mentioned type I thyroplasties, the success depends on the correct
size (Koufman formula) [53] and placing
of the thyroid cartilage window. To avoid a extrusion of the foreign
material into the endolarynx, a too high stamp pressure on the tissue and
sharp edges should be avoided. This technique should only be performed by
very experienced laryngologists. Only non-reinforced, medical grade silicone
blocks should be used as the base material for the intraoperative cutting of
these implants.
Fig. 4 Principle of medialization thyroplasty (ML) with
thyroplasty window creation and silicone wedge (white wedge).
The advantage of pre-shaped silicone wedges is that measures proven in
studies are kept so that insertion may be performed with individually cut
implants based on templates [56]
[57]. This also includes the pre-shaped,
but individually adaptable Netterville PhonoForm silicone blocks [58] that are distributed by Medtronic
Company. These products are FDA approved, but not CE certified.
Silastic implants that have been specifically developed for thyroplasty
provide a better patient safety since they have round edges and an
integrated dislocation protection. They may be chosen in 6 sizes (for males
and females each) based on a test stamp range (Montgomery Thyroplasty
Implant System) [59]
[60]. For this implant, investigations
about the biocompatibility are available and they are CE approved so that
they may be applied in-label.
1.2.3 Ceramic implants
In 1993, Cummings, Purcell, and Flint developed an implant system for
thyroplasty made of hydroxyl apatite in 6 different prefabricated sizes
[61]. As of the beginning of the
1990s, hydroxyl apatite became widely distributed as bone graft substitute
in medicine and dentistry. The material disposes of good biocompatibility
and stability. With this implant, the first-describing authors wanted to
imitate the firm cartilage-bone structure of the thyroid cartilage and
secure a safe anchoring at the thyroid. Extrusions and postoperative
swelling have been described in the introduction phase [62].
Test stamps of 3–8 mm penetration depth may be inserted via a
standard thyroplasty window for medialization of the vocal fold. The stamp
with the best endoscopically or auditively controlled medialization effect
assessed under local anesthesia is chosen as ceramic implant and secured
with the according locking clip. The implant system is distributed by
Olympus Company under the brand name of VoCom and is CE certified. In
Germany, the system is not widely used.
1.2.4 Titanium clips
In 1996, Friedrich developed the Titanium Vocal Fold Medializing Implant
(TVFMI) in cooperation with Heinz Kurz Company (Dusslingen, Germany) [63]. The clip that is made of medically
pure titanium was intended to reduce the time efforts for the surgeons like
other pre-shaped implants. It shows a stable mechanical and functional
medialization effect [64]. In
comparison to silicone implants, titanium clips have better functional
results, however, they are not statistically significantly better [65]
[66]. The long-term results are stable [67]. For TVFMI as well, single reports
about extrusions and dislocations have been published. In Austria and
Germany, the system is widely used.
1.2.5 Secondarily adjustable implants
Up to now, none of the described implants could reveal a general superiority
over other implants. Considering critically the long-term results of
medialization thyroplasty with silicone, ceramic, titanium, and autologous
implants, the revision rate in larger trials varies between 5.4% and
33% [68]
[69]. According to a USA wide survey
performed by Rosen [69], the reasons
for revision were predominantly the under-correction and/or the
decreasing glottic closure (33%). According to Woo, the remaining
glottic insufficiency refers the posterior third with 55% [70]. In this study, cases with
preoperatively severer posterior glottic gap that have already been combined
treated initially with arytenoid adduction are not taken into account. Only
in 6% of the cases, the implant had to be replaced with a smaller
one due to over-correction [69]. In
8%, repositioning was necessary [69]. In revision cases, dynamic computed tomography trials in
phonation show an under-correction of up to 75% in thyroplasty,
followed by a too high or regarding the vocal fold axis angled position of
the implant [71]. Consequently, the
exact positioning of the thyroid cartilage window and the individual
adaptation of the implant size has a particular significance in order to
achieve optimal voice improvement and to avoid revision surgery. The
surgical exposition, the exchange or repositioning of thyroplasty implants
are associated with higher complication rates with regard to airway
obstruction, swallowing disorders, hematoma, and thyroid cartilage stability
[72].
Therefore, the wish to develop secondarily adjustable implants for
thyroplasty was stated. The first implant of this type was the Thyroprotip
titanium implant with an adjusting screw and a stamp made of titanium pearls
welded together that should secure the ingrowth of connective tissue and
thus an intensive adhesion with the paraglottic soft tissue [73]. With this adjustable implant, it
was possible during revision to increase or reduce the stamp effect without
removing the anchoring of the implant body in the thyroid cartilage. This
method was CE certified. However, the implant, probably due to the takeover
of the Protip Company, was not further developed and new results are not
available.
Consequently, the approach of secondary adjustability and the securing of
optimal window position was recently pursued by Ho et al. [74]. The VOIS Implant in 4 different
sizes and the according instrument set for positioning the thyroid cartilage
window is a CE approved secondarily adjustable implant system. It combines
the advantages of a titanium corpus anchoring in the thyroid that is easy to
implement and dislocation-safe with a tissue-friendly silicone pad for
individual medialization of the vocal fold. After choosing the appropriate
size of the implant based on the sex and the thyroid ala length, the
silicone pad can be re-filled with NaCl under endoscopic control according
to the necessary stamp effect. Without re-surgery, the micro port located at
the outside of the thyroid cartilage may be punctured under ultrasonographic
control and the filling volume of the silicone pad may be adjusted in cases
of over- or under-correction (see [Fig.
5]). Another significant advantage of this implant is the vector
of the expanding silicone pad. While the flank of the implant medializes the
vocal fold, the tip of the silicone pad displaces the vocal process in
medio-dorsal direction so that an additional intervention for arytenoid
adduction is possibly no longer necessary.
Fig. 5 Medialization thyroplasty (ML) with effect on the
arytenoid position with a secondarily adjustable composite implant
(VOISImplant), the silicone pad that may be refilled with NaCl is
depicted in grey.
1.3 Arytenoid adduction and cricothyroid subluxation
Recurrent laryngeal nerve paralysis affects all inner laryngeal muscles of the
respective side. Depending on the severity of the damage of the single muscles,
the predominant findings consist of vocal fold bowing due to a damaged
thyroarytenoid muscle (TA) or pathologic intermediate or lateral position due to
failure of the lateral cricoarytenoid muscle (LCA). The weakness of the
posterior cricoarytenoid muscle (PCA) does not only inhibit the opening of the
glottis but also reduces the counter-tension at the arytenoid cartilage against
the tension of the non-affected cricothyroid muscle (CT). As a consequence, the
vocal process is displaced in anterior direction with shortening of the vocal
fold. The interarytenoid muscles (IA) getting bilateral innervation. Unilateral
paralysis leads to incomplete closure in the area of the posterior commissure,
mostly rather due to the anterior-cranial tilting of the arytenoid cartilage
(LCA/PCA effect) than due to IA weakness. Recurrent laryngeal nerve paralyses
with severe LCA weakness and tilting of the arytenoid cartilage cause an
relevant posterior glottis gap that cannot be corrected with standard ML alone.
Therefore, Isshiki introduced arytenoid rotation in addition to thyroplasty type
I already in 1978 [75]. By means of two
non-absorbable threads at the muscular process of the arytenoid cartilage
pulling to the anterior inferior edge of the thyroplasty window, he mimicked the
effect of the LCA and rotated the vocal process in medio-caudal direction. That
is why this procedure is also called arytenoid adduction (AA). A series of
modifications were related to the traction direction of the thread to a fixation
point that is located even more anterior-medio-caudally below the insertion of
the vocal fold at the inferior edge of the thyroid cartilage [76]. Other modifications concerned the
position and size of the additional cartilage window at the posterior edge of
the thyroid [77] and less invasive
approaches to position the thread, e. g., the sling or string pull
technique described by Hess [78]
[79]. AA is technically more complex, and the
combination of ML with AA is associated with a clearly higher risk of hospital
re-admission within 30 days [80]. Specific
risks of AA are postoperative bleeding, posterior laryngeal swelling with
temporary swallowing problems and risk of aspiration, and perforation of the
hypopharynx. The surgery is irreversible because the lateral joint capsule is
opened for mobilization resulting in a fixation of the cricoarytenoid joint
(CAJ). In the context of AA, synkinetic nerve fibers may be transected due to
the close neighborhood of the recurrent laryngeal nerve to the CAJ, possible
leading to further tension loss and atrophy of the vocal fold.
The additional functional gain by combining ML with AA could only be shown in
studies that have performed stratification based on a large posterior glottis
gap or high voice-related handicap (VHI) [81]. In all other cases, ML alone could achieve sufficient voice
improvement [82]. The definition of a
large posterior glottis gap is not clear in the literature. According
to Yilmaz and Özer, the gap should only be classified as large when the
vocal process remains in abduction position during phonation [83].
In 1998, Zeitels et al. introduced a therapeutic option called Adduction
Arytenopexy (AApexy)
[84]. With this
procedure, the correct position of the arytenoid should be achieved as in AA and
at the same time the length and tension of the vocal fold should be increased.
The CAJ is opened more widely, and the muscular process of the arytenoid
cartilage is fixed at the cricoid plate after medio-cranio-posterior
displacement. This interesting method requires an even more extensive posterior
exposition of the larynx and the complication risks become more significant. Due
to the complexity of the intervention and the mentioned risks, AApexy could not
prevail like the so-called Cricothyroid Subluxation that had been
introduced by the same team [85]. This
procedure consists of opening the cricothyroid joint, and a suture pulls the
inferior horn of the thyroid cartilage in anterior direction to the cricoid arch
so that the paralyzed vocal fold is tightened.
Apart from AA, an innovative approach for endoscopic correction of the vocal fold
position has recently been presented by Rovo et al. [86]. The authors manually reposition the
arytenoid cartilage in the context of microlaryngoscopy and fix the position by
means of fat injections laterally to the vocal process and the arytenoid body.
The long-term results of this method must be awaited.
Unfortunately, the application of AA and the surgical experience with AA in the
USA and in Europe is continuously decreasing during the last 10 years [87].
1.4 Other procedures and outlook
Re-innervation of the paretic laryngeal muscles can be done without the use of
biomaterials. Already in 1925, Colledge made first successful attempts to
anastomose the recurrent laryngeal nerve (RLN) stump with the vagus stem or the
phrenic nerve in monkeys [88]. Tucker was
the first to describe the nerve-muscle pedicle re-innervation of the PCA in 1976
[89] and in 1977 the re-innervation of
the LCA with this method [90]. In 1984,
Crumley introduced the concept of selective re-innervation by anastomosing the
ansa cervicalis with the RLN adductor terminal branches and phrenic nerve fibers
to the RLN abductor branches [91]. These
complex and risky surgeries are usually not required in cases of unilateral
paralyses. Based on this concept, Crumley described the partial step of
anastomosing the ansa cervicalis with the RLN stem as non-selective
re-innervation (NSR) in 1988. With this method, the objective of recovered
motility of the vocal fold was abandoned. The re-toning and medialization of the
paralyzed vocal fold became the primary objective. Thus, this procedure
represents an alternative to ML. If implants are not used, foreign body
reaction, extrusion, or dislocation can be avoided. Furthermore, the vibrating
ability of the vocal fold is not impaired by inserted biomaterials. The
functional advantage of NSR that is less known in Europe compared to ML, is
currently investigated in a British phase-2 study (VOCALIST) [92]. Our own experience with a modified NSR
performed in contrast to Kodama [93]
without AA, showed good toning of the vocal fold after 3–4 months. In
our method the transection of the RLN that still has a remaining function after
synkinetic re-innervation is avoided. An additional adductive innervation to
TA/LCA is provided by an ansa-nerve-muscle pedicle inserted via a
thyroid cartilage window. In contrast to ML, the position and the tonus of the
vocal fold improved further after 12 months and up to 24 months with excellent
voice quality [94].
In the future, the neurostimulation of a synkinetically re-innervated
TA/LCA complex might provide another alternative for ML in cases of
particular voice requirements (e. g. singers, speaking professionals)
[95]. Electrical impulses that are
delivered synchronously to the adduction of the healthy vocal fold can elicit
the contraction of a synkinetically re-innervated vocal fold [96].
The disadvantage of all static medialization techniques of paralyzed vocal folds
is the permanent reduction of the glottic gap that becomes a breathing
limitation for patients with high respiratory requirements [97]
[98]. By means of functional electrical stimulation, the vocal fold
remains in a more favorable position for respiration and is active adducted
during phonation.
However, this is still an innovative research approach. In the upcoming years, an
approved medical product will probably not be available yet. However, first
clinical experiences with neurostimulation in cases of bilateral paralysis (see
next chapter) are promising [99]
[100].
Another field for research and development regarding the assessment and
comparability of the results of surgical procedures in cases of unilateral RLN
paralysis is the improvement of the objectiveness and reproducibility of
laryngo-stroboscopic findings. Bakhsh et al. could show that the multitude of
parameters to describe the vocal fold position or the glottis gap combined with
unmatched grading systems make the comparability of the study results more than
difficult [101]. Only 7 of 21 investigated
laryngo-stroboscopic parameters confirmed obvious postoperative differences
compared to the preop condition. Surprisingly, the periodicity and the bowing of
the vocal fold were more significant than the glottis gap during phonation.
Functional parameters like the maximum phonation time (MPT) or the questionnaire
on the voice handicap (VHI) could be reproduced clearly more easily.
